1. Field of the Invention
The present invention relates to a non-impact printer, and more particularly to a printer wherein a printing is performed in a dot configuration on each line perpendicular to a sheet running direction.
2. Description of the Prior Art
Hitherto, in a non-impact printer such as an electrophotographic printer, an electrically charged photoconductor drum is illuminated by with a light source to form an electrostatic latent image on a surface thereof, a developing is performed upon adhesion of a toner to the electrostatic latent image, to form a toner image, and then the thus obtained toner image is transferred to a recording material to be fixed thereon.
FIG. 2 is a block diagram of a printer control circuit in a conventional non-impact printer. In FIG. 2, a control unit 1 transmits, at the time point that a sheet arrives at a printing ready point, a timing signal 12, including a line and a raster timing signal, to another controller, and receives a video signal 11 which has been edited on each page in the other controller. The received video signal 11 in the control unit 1 is transmitted to a print head 19 in the form of a real printing data signal 18. Upon receipt of a line of video signal 11, the control unit 1 transmits a latch signal 17 to a print head 19 so as to hold the real printing data signal 18 therein. Before receiving the subsequent data from the other controller, the thus held real printing data signal 18 is visualized in print when the print head 19 receives a printing drive signal 13.
Transmission and receipt operations of the video signal 11 are performed in units of print lines. FIG. 3 is an operational time chart of the conventional non-impact printer as mentioned above. In a case where a tone expression according to the dither pattern is performed, the number of dots to be printed per unit area is increased or decreased in accordance with a density or concentration of the image. In this case, regarding the dots for use the tone expression and the dots constituting part a character, a line and the like, one designs in such a manner that an even energy is given at the time of printing to drive the segments of the print head corresponding to the respective dots.
Further, in case of printing of a character and the like according to the non-impact printer as mentioned above, it is necessary to form a continuous line, and thus in accordance with such a printer, adjacent dots are printed on an overlapping basis, but not to form individual dot trains. For example, the a case where printing data representing dots as shown in FIGS. 6 and 8 are arranged, the adjacent dots are in fact printed to overlap one another, as shown in FIGS. 7 and 9, respectively.
However, according to the conventional non-impact printer as mentioned above, in a case where a slash extending in a lateral direction is printed, the printed slash provides, as shown in FIG. 4, a polygonal or broken line-like image rather than a straight line-like image, in view of a relation between a raster interval and a dot interval.
Also, as shown in FIG. 5, in the case where printing is performed as a dashed or broken line coupling dot D1 with dot D5, dot D3 forms a straight line-like image since it locates on a lattice L20 of a basic raster line 102. However, there are not any suitable dot positions for interpolation between dots D1 and D3 and also between dots D3 and D5, so that dots D2 and D4 are actually printed thereby providing a polygonal line-like image. Similarly, in a case where printing is performed as a broken line coupling dot D6 with dot D10, dot D8 forms a straight line-like image together therewith. However, dots D7 and D9 result in providing a polygonal line-like image.
Further, according to the conventional non-impact printer as mentioned above, there is designed such a printer that an even energy is given in both of the cases of printing of the dots for use in the tone expression and printing of the dots constituting part of a character, a line and the like. Thus, if an optimum driving energy is set for one of the printings, a driving energy for the other printing is not an optimum value. As a consequence, the tone expression is far from the ideal one, thereby becoming dark.
Furthermore, in the case where a high duty printing is performed in accordance with the conventional non-impact printer of the type mentioned above, that is, in a case where a printing is performed which is extremely full of the number of dark dots in a printed picture, such as a reversed printing, the area of a non-printed part is small so that an unfocused image and discontinuity would occur.